In modern high speed sheet processing machines such as printers, sorter, collators, reproduction machines, etc. a sheet mis-feed or multi-fed sheets can seriously impair the operation of the machine. Numerous devices such as belt feeders of the type disclosed in U.S. Pat. No. 3,768,803 or impact/paddle feeders of the type disclosed in U.S. Pat. No. 3,630,516 have been employed to minimize the possibility of mis-feeds and multi-feeds.
It is common practice to provide sheet feeding devices wherein the sheet separator is disposed at the top of the stack, a sheet elevator assembly being utilized to continuously shift the stack in an upward direction to maintain the top sheet in the stack adjacent the feed mechanism. While a bottom feed device is more convenient since the stack may be replenished without stopping machine operation and the necessity of an elevator type sheet tray is obviated, the poor paper feeding capabilities of bottom feed devices has prevented common acceptance thereof. To improve the paper feeding capabilities of bottom feeders, the air floatation principle has been employed to "lift" the stack from the bottom sheet to allow the bottom sheet in the stack to be easily separated therefrom. The air floatation feature also provides "inter-sheet" lubrication by air for ease in sheet separation.
The aforementioned impact feeders or "inertia feeders" have been employed in top sheet feed devices in an attempt to overcome inter-sheet friction and assure positive feeding of sheets by jarring or impacting the sheet to be fed, thereby breaking the inter-sheet friction between the sheet being fed and the adjacent sheets. However, in impacting the sheets, there is a tendency for the impacting device to jam the sheet to be fed into tighter engagement with the remainder of the sheets in the stack, thereby obviating the benefits obtained in attempting to impact the sheet in the feed direction, off from the remainder of the sheets in the stack.